Field of the Invention
The present disclosure relates to a sheet conveying apparatus that conveys sheets in a continuous manner, an image forming apparatus, such as a copier, a printer, or a facsimile, that includes the sheet conveying apparatus, and an image reading apparatus.
Description of the Related Art
In recent years, measures further saving resources are awaited in image forming apparatuses and double-side printing on sheets, such as paper, an overhead projector (OHP) sheet, a plastic sheet, and fabric, is frequently performed. Accordingly, in an image forming apparatus that has a double-side printing function, importance is placed on improving the number of sheets that is output per unit time during double-side printing, in other words, importance is placed on improving the productivity of both-side printing.
As a known art, a configuration is disclosed in Japanese Patent Laid-Open No. 2015-083353 in which a group of reversing rollers that includes a single driving roller that receives a driving force and that rotates in only one direction, a first driven roller, and a second driven roller is provided in a reversing unit that reverses a sheet. Regarding the configuration of the group of reversing rollers, the three rollers are arranged in the order of the first driven roller, the driving roller, and the second driven roller so as to be aligned on a substantially straight line in a direction intersecting a sheet conveying direction. The first driven roller opposing the driving roller forms a first nip portion, and the second driven roller opposing the driving roller in a direction different from that of the first driven roller forms a second nip portion.
Sheet reversing is performed in the following manner in the reversing unit in Japanese Patent Laid-Open No. 2015-083353. A sheet, on which an image has been formed on a first surface, is first conveyed towards the first nip portion in the group of reversing rollers. Subsequently, in the first nip portion, the sheet is conveyed in a first direction that is a direction in which the sheet is discharged from the group of reversing rollers, and a rear end of the sheet in the sheet conveying direction passes the first nip portion. A switchback portion that temporarily accommodates the sheet is provided in the reversing unit at a portion downstream of the first nip portion in the sheet conveying direction, and the sheet that has passed the first nip portion is accommodated in the switchback portion. Subsequently, by having the sheet accommodated in the switchback portion fall by its own weight, the rear end of the sheet is guided to the second nip portion in the group of reversing rollers. Since the driving roller rotates in only one direction, the sheet pinched by the second nip portion is conveyed in a second direction that is a direction opposite the first direction, which is the conveying direction in the first nip portion. Subsequently, the sheet is conveyed to the image forming unit once again and after an image is formed on a second surface of the sheet, the sheet is conveyed to a sheet discharge unit that is provided at a position that is different from that of the reversing unit. Subsequently, the sheet is discharged from the inside of the image forming apparatus with discharge rollers of the sheet discharge unit.
However, in the configuration of Japanese Patent Laid-Open No. 2015-083353, since the reversing of the sheet is performed by moving the rear end of the sheet to the second nip portion with the weight of the sheet itself after the sheet is completely discharged from the first nip portion in the group of reversing rollers to the switchback portion, the following issue occurs. That is, the timing at which the sheet is reversed (the timing from when the sheet passes through the first nip portion until the sheet is pinched by the second nip portion) may greatly differ due to the difference in the sheet thickness or the sheet grammage, or whether there is a flexure (curl) in the sheet. In such a case, the sheet conveying timing may be off with respect to a predetermined timing, or the interval (sheet interval) in which the sheets are conveyed when the sheets are conveyed successively may be off with respect to a predetermined interval, which may lower the sheet conveying performance.